MISCIBILITY OF PHOSPHOLIPIDS AND CHOLESTERYL ACETATE IN MIXED MONOLAYERS ON AQUEOUS SURFACES

The surface pressure - area per molecule curves (F A curves) of mixed monolayers of phosphatidyl serine (PS) and cholesteryl acetate (CA), and those of dimyristoyl phosphatidyl choline (DMPC) and CA were measured on aqueous surfaces. Those F - A curves showed kink points, which were considered to be the collapse point of the monolayers. Then, the collapse pressure was determined as the surface pressure at the collapse points. On the basis of the phase diagrams, drawn by plotting the measured values of the collapse pressure as a function of the composition, the miscibility of the lipids in the mixed monolayers was discussed. Thus, it has been concluded that PS and CA, and also DMPC and CA are completely miscible in the monolayers on water. On the other hand, it has been also found that, on aqueous solutions of 100 mM CaCl2, PS and CA are immiscible in the monolayers because of the aggregation of PS molecules induced by Cat2+. © 1979 Dr. Dietrich Steinkopff Verlag.